The following projects will be investigated: (1) An intensive characterization will be made of a new 200 kilodalton intracellular protein we have recently isolated from cardiac muscle cell membranes (fascia adherens), that also is found at the focal adhesions of cultured fibroblasts. We will determine if this protein is an in vivo substrate for p60src in Rous sarcoma virus-tranformed fibroblasts. (2) We will further characterize a set of 30 monoclonal antibodies we have prepared, all of which inhibit the attachment of fibroblasts to their substrata. The localization of these antibodies on the fibroblast surface will be studied by immunofluorescence and immunoelectron microscopy. The antigens specific for these monoclonal antibodies will be detected by immunoprecipitation and immunoblotting experiments. (3) Mice will be immunized with the purified fascia adherens membranes of chicken cardiac muscle cells, and monoclonal antibodies will be produced from splenic cell fusions which will be screened for their immunolocalization to various cell-cell contact sites.